Fullmetal Alchemist Brotherhood ED: Adventure Time remake

The first ending sequence of Fullmetal Alchemist Brotherhood remade with the world and characters of Adventure Time.
A fan creation made with love, Movie Maker and suffering (in this order).

See original:    • FullMetal Alchemist Brotherhood ED 1  
Song: Uso by SID
Original sequence animated by Morii Kenshirou

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EDIT 2: HOW THIS WAS MADE:
(TL;DR: I drew everything in PaintTool SAI (version 1))

I have been seeing many comments asking me how this animation was done, so I will try to answer that question.
Disclaimer: The process I am about to describe was inefficient and rather stupid. If you're an aspiring animator, take it as an example of what NOT to do!

(Although this video was uploaded in 2021 (or just made public, I forget), it was actually finished in 2020 and started in 2017. (However I wouldn't say I spent three years on it, it was only a few months in total interrupted by long periods of time I didn't work on it at all.) So it's been a while now and I don't remember every detail of the creation process.)

All of the art was made in PaintTool SAI (version 1). I had the original Fullmetal Alchemist Brotherhood ED sequence open in Movie Maker on the side, so I could analyze it frame by frame and essentially copy the key frames, and a lot of the in-between ones too. (The goal was to make it look and feel exactly like the original with a different coat of paint, so there was a lot of copying involved. (Although you can see there are also multiple bits of original animation!))
Every single frame was drawn in PaintTool SAI then exported into a BMP image file, and every BMP image was put into Pencil, a free animation software. The reason I didn't draw directly into Pencil I believe was that it didn't have any brushes that could replicate the style of the original ED. (Also, I used to do everything in PaintTool SAI because it was what I knew and was comfortable with. Essentially I was too lazy or stubborn to find a better smarter way to do this.)
Every time an image had to slide across the screen without being redrawn, I was drag-and-dropping it for every frame and counting the pixels to make sure the motion would come out smooth. (Don't do that.)
I was getting pretty tired of everything near the end (I made everything chronologically) and I was really looking forward to finishing it, so that's why for example I ended up not including the cat from the original sequence near the end. I also didn't really know what to replace it with, I considered the cat assassin character who stays in Jake's ear in that one episode (hopefully I am remembering that correctly) but also felt like she was too obscure of a character.
Pencil couldn't handle too many images inside one project so I split everything into five projects. Then because I couldn't figure out how to export video in Pencil, I ran the sequences still inside the program while I recorded it with OBS, then I put all the sequences together in Movie Maker, then of course I added the song.

And there you go! Maybe that was more of a blog-posty story about a silly amateur animator who doesn't know how to use a computer than an explanation of how I made this video. But hopefully you can take something positive from it.
If I see further questions I will try to answer them.

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(EDIT 1: To be clear because I saw that some people in the comments were confused, I did animate this. It is entirely based on the first ending sequence of Fullmetal Alchemist Brotherhood and uses characters from Adventure Time. I did not make the song, it was made by SID.)